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130 lines
6.2 KiB
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<H3>atom_style command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>atom_style style args
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</PRE>
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<UL><LI>style = <I>angle</I> or <I>atomic</I> or <I>bond</I> or <I>charge</I> or <I>dipole</I> or <I>dpd</I> or <I>ellipsoid</I> or <I>full</I> or <I>granular</I> or <I>molecular</I> or <I>peri</I> or <I>hybrid</I>
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</UL>
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<PRE> args = none for any style except <I>hybrid</I>
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<I>hybrid</I> args = list of one or more sub-styles
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</PRE>
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<P><B>Examples:</B>
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</P>
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<PRE>atom_style atomic
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atom_style bond
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atom_style full
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atom_style hybrid charge bond
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Define what style of atoms to use in a simulation. This determines
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what attributes are associated with the atoms. This command must be
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used before a simulation is setup via a <A HREF = "read_data.html">read_data</A>,
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<A HREF = "read_restart.html">read_restart</A>, or <A HREF = "create_box.html">create_box</A>
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command.
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</P>
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<P>Once a style is assigned, it cannot be changed, so use a style general
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enough to encompass all attributes. E.g. with style <I>bond</I>, angular
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terms cannot be used or added later to the model. It is OK to use a
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style more general than needed, though it may be slightly inefficient.
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</P>
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<P>The choice of style affects what quantities are stored by each atom,
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what quantities are communicated between processors to enable forces
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to be computed, and what quantities are listed in the data file read
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by the <A HREF = "read_data.html">read_data</A> command.
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</P>
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<P>These are the additional attributes of each style and the typical
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kinds of physical systems they are used to model. All styles store
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coordinates, velocities, atom IDs and types. See the
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<A HREF = "read_data.html">read_data</A>, <A HREF = "create_atoms.html">create_atoms</A>, and
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<A HREF = "set.html">set</A> commands for info on how to set these various
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quantities.
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</P>
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<DIV ALIGN=center><TABLE BORDER=1 >
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<TR><TD ><I>angle</I> </TD><TD > bonds and angles </TD><TD > bead-spring polymers with stiffness </TD></TR>
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<TR><TD ><I>atomic</I> </TD><TD > only the default values </TD><TD > coarse-grain liquids, solids, metals </TD></TR>
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<TR><TD ><I>bond</I> </TD><TD > bonds </TD><TD > bead-spring polymers </TD></TR>
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<TR><TD ><I>charge</I> </TD><TD > charge </TD><TD > atomic system with charges </TD></TR>
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<TR><TD ><I>dipole</I> </TD><TD > charge and dipole moment </TD><TD > atomic system with dipoles </TD></TR>
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<TR><TD ><I>dpd</I> </TD><TD > default values, also communicates velocities </TD><TD > DPD models </TD></TR>
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<TR><TD ><I>ellipsoid</I> </TD><TD > quaternion for particle orientation, angular momentum </TD><TD > aspherical particles </TD></TR>
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<TR><TD ><I>full</I> </TD><TD > molecular + charge </TD><TD > bio-molecules </TD></TR>
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<TR><TD ><I>granular</I> </TD><TD > diameter, density, angular velocity </TD><TD > granular models </TD></TR>
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<TR><TD ><I>molecular</I> </TD><TD > bonds, angles, dihedrals, impropers </TD><TD > uncharged molecules </TD></TR>
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<TR><TD ><I>peri</I> </TD><TD > density, volume </TD><TD > mesocopic Peridynamic models
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</TD></TR></TABLE></DIV>
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<P>All of the styles define point particles, except the <I>ellipsoid</I> and
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<I>granular</I> and <I>peri</I> styles. These define finite-size particles.
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For <I>ellipsoidal</I> systems, the <A HREF = "shape.html">shape</A> command is used to
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specify the size and shape of particles, which can be spherical or
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aspherical. For <I>granular</I> systems, the particles are spherical and
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each has a specified diameter. For <I>peri</I> systems, the particles are
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spherical and each has a specified volume.
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</P>
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<P>All of the styles assign mass to particles on a per-type basis, using
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the <A HREF = "mass.html">mass</A> command, except the <I>granular</I> and <I>peri</I> styles.
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For <I>granular</I> systems, the specified diameter and density are used to
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calculate each particle's mass. For <I>peri</I> systems, the speficied
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volume and density are used to calculate each particle's mass.
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</P>
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<P>Only the <I>dpd</I> and <I>granular</I> styles communicate velocities with ghost
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atoms; the others do not. This is because the pairwise interactions
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calculated by the <A HREF = "pair_dpd.html">pair_style dpd</A> and <A HREF = "pair_gran.html">pair_style
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granular</A> commands require velocities.
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</P>
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<HR>
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<P>Typically, simulations require only a single (non-hybrid) atom style.
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If some atoms in the simulation do not have all the properties defined
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by a particular style, use the simplest style that defines all the
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needed properties by any atom. For example, if some atoms in a
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simulation are charged, but others are not, use the <I>charge</I> style.
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If some atoms have bonds, but others do not, use the <I>bond</I> style.
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</P>
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<P>The only scenario where the <I>hybrid</I> style is needed is if there is no
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single style which defines all needed properties of all atoms. For
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example, if you want charged DPD particles, you would need to use
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"atom_style hybrid dpd charge". When a hybrid style is used, atoms
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store and communicate the union of all quantities implied by the
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individual styles.
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</P>
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<P>LAMMPS can be extended with new atom styles; see <A HREF = "Section_modify.html">this
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section</A>.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>This command cannot be used after the simulation box is defined by a
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<A HREF = "read_data.html">read_data</A> or <A HREF = "create_box.html">create_box</A> command.
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</P>
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<P>The <I>angle</I>, <I>bond</I>, <I>full</I>, and <I>molecular</I> styles are part of the
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"molecular" package. The <I>granular</I> style is part of the "granular"
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package. The <I>dpd</I> style is part of the "dpd" package. The <I>dipole</I>
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style is part of the "dipole" package. The <I>ellipsoid</I> style is part
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of the "asphere" package. The <I>peri</I> style is part of the "peri"
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package for Peridynamics. They are only enabled if LAMMPS was built
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with that package. See the <A HREF = "Section_start.html#2_3">Making LAMMPS</A>
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section for more info.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "read_data.html">read_data</A>, <A HREF = "pair_style.html">pair_style</A>
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</P>
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<P><B>Default:</B>
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</P>
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<P>atom_style atomic
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</P>
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</HTML>
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